1. Field of the Invention
The present invention is related to an optical encoder employing an optical scale for measurement of displacement such as the amount of shift or amount of rotation of the measured object, and particularly to an optical encoder with simple composition which can simultaneously detect the direction of displacement of a measured object.
2. Related Background Art
The so-called optical encoder which detects the amount of shift or rotation of the measured object utilizing an optical scale has been proposed before, for example, in U.S. Pat. No. 3,856,401, Japanese Laid-Open Patent Application Nos. 59-63517 and 60-140119.
For example, U.S. Pat. No. 3,856,401 proposes the optical encoder which employs the optical scale comprising a grooved lattice having a groove of triangular section composed of a light transmission member. According to the publication, two phase output signals (two phase signal of push-pull output) having an electric phase difference of 180.degree. are taken out as the output signal by detecting the light beam projecting in two directions at the inclined surface of the triangular groove by two light receiving devices individually.
However it was not a preferred method because the optical encoder of the publication must be provided with adjusting means to equalize the relative intensity of the two phase output signals in order to obtain the two phase output signals having the phase difference of 90.degree..